Semiconductor wafer manufacturing processes are complex and include a plethora of processing steps. These processing steps are, during each of the sequences that are executed as part of the step, closely monitored and may result in a complex web of rework, rejects, partial rework, etc. This invariably results in many diverse flows of partially completed wafers, as opposed to the ideal processing sequence where a wafer proceeds from known step to known step.
Wafers may repeat prior process steps causing concerns of wafers downstream in the processing line to be contaminated with wafers that have already undergone more advanced steps of processing.
It is appropriately important to screen for such occurrences and to limit or eliminate the impact of contamination that may be introduced into a wafer processing operation by wafers that are not part of the regular wafer process flow.
During normal wafer processing, meticulous attention is paid to maintaining a clean, particle free environment. This clean environment has a direct impact on wafer yield and cost. Wafer processing by its very nature tends to introduce impurities into the processing environment; these impurities can for instance be introduced from wafer processing furnaces, by way of example.
In point of fact, particles may diffuse into the semiconductor substrate, especially in areas of the manufacturing process where high frequency operations are being performed on the substrate. This can have a severe detrimental effect on wafer properties making these wafers unsuitable for further use.
In other cases, donor or acceptor dopants may be introduced to substrates. These dopants can have a direct affect on the performance of the devices that are at a later stage to be created from these wafers. Alternatively, other impurities can cause surface defects in the wafer or stacking faults or dislocations in the atomic structure of the substrate. For instance, poor wafer surface can be caused by organic matter that is present in the wafer-processing environment, such as oil or oil related matter.
All possible impurities must be carefully monitored and controlled and must, when present, be removed from the wafer processing environment. This control must be exercised within the cycle of wafer processing steps and at the beginning of the wafer manufacturing process.
The frequency and intensity of such contaminant control operations is highly cost dependent and should, wherever possible, be performed at as low a cost as can be accomplished. Methods of identification and elimination must therefore be simple but effective. Processing conditions and environments can lead to the introduction of a large number of contaminants and therefore lead to the need for strict control of the environment and the way in which the wafers that are being processed are being routed.
Among the contaminants that can accumulate on the surface of a substrate are metals, such as copper, aluminum or the like. Control mechanisms that enhance the monitoring of the level of metal deposited on the surface of a wafer prevent unnecessary rerouting and rework of such wafers. Production cost of semiconductor wafers will be reduced if such wafers can be identified so that only wafers that need to be rerouted for rework are entered into the rework cycle.
There is therefore a need in the art for a system for detecting metal content of a semiconductor surface and method for operating the same, particularly, to detect deposited or sputtered metal layers on all forms of wafer substrates.